Molybdenum-hafnium alloy casting



United States Patent the Public Claims. (Cl. 75176) This application is a continuation-in-part of applicants application Serial No. 41,766, filed July 11, 1960, now abandoned, which was a continuation-in-part of application Serial No. 760,066, filed September 10, 1958, and now abandoned.

The present invention relates to cast molybdenum base alloys containing hafnium and which are characterized by the fact that they are capable of being worked at elevated temperatures and have unusually high strength at temperatures in the range of 1600 F. and above.

The alloys of the present invention contain from .02% to 12% hafnium and up to .75 carbon, preferably 01% to .04% carbon. The balance consists essentially of molybdenum, except that small quantities of titanium and/ or zirconium may be present as optional ingredients. Thus, titanium may be present in amounts up to but not more than 5% and zirconium in amounts up to 1%. In addition, a portion of the molybdenum may be replaced by tungsten up to a total not exceeding the molybdenum present. Since even the smallest amount of oxygen is deleterious, the oxygen content of the alloys must be less than 005% and is preferably less than 002%.

The alloys of the present invention may be prepared by arc-melting in vacuum, preferably using a furnace of the type disclosed in United States Patent 2,656,743. The preferred method of deoxidizing the melt is by adding carbon to the charge to react with any oxygen present in raw materials and in quantities which will leave the desired excess in the final casting. The absolute pressure during the melting operation is preferably maintained below 50 microns of mercury.

The following are specific examples of alloys coming within the scope of the present invention:

A twelfth example of an alloy containing both the optional ingredients titanium and zirconium is an alloy containing .14% hafnium, 148% titanium, .077% zirconium, .02% carbon and the balance consisting essentially of molybdenum.

In cases where a higher melting point or slightly higher strength in a recrystallized state at temperatures above 2000 F. is desired, any of the above examples may have up to one-half of the molybdenum replaced by tungsten. In alloys such as the present, in which substantial quantities of molybdenum are employed, the use of larger quantities of tungsten should be avoided because of forging difiiculties. In addition, it is preferred that the maximum hafnium content decrease proportionately from 12% to 1% as the tungsten content increases toward equality with the molybdenum.

Patented Feb. 16, 1965 The high strength of the alloys of the present invention will be apparent from the fact that the alloy of Example 1 has a tensile strength of 66,300 pounds per square inch at 1600 F the alloy of Example 3 has a tensile strength of 74,900 pounds per square inch at 1600 F.; the alloy of Example 8 has a tensile strength of 85,100 pounds per square inch at 1800 F.; and the alloy of Example 12 has a tensile strength of 85,200 pounds per square inch at 1800 F. The tensile strength figures given above are all applicable to the forged alloys in a stress-relieved condition.

The alloys of the present invention may be forged or worked at temperatures in the neighborhood of 2300 F. or above.

All proportions given are proportions by weight.

What is claimed is:

1. A cast alloy containing from .02% to 12% hafnium, .01% to .75% carbon, less than 005% oxygen, not more than 5% titanium, not more than 1% zirconium, and the balance consisting essentially of a member from the group consisting of molybdenum and mixtures of molybdenum and tungsten wherein the molybdenum content is at least equal to the tungsten content.

2. A cast alloy containing from .02% to 12% hafnium, 01% to .75 carbon, less than 005% oxygen, and the balance consisting essentially of molybdenum.

3. A cast molybdenum alloy capable of being worked at elevated temperatures and containing from .02% to 12% hafnium, not more than .75 carbon, less than .005 oxygen, not more than 5% titanium and not more than 1% zirconium, the balance consisting essentially of a member from the group consisting of molybdenum and mixtures of molybdenum and tungsten wherein the molybdenum content is at least equal to the tungsten content, and the maximum hafnium content being reduced proportionately from 12% to 1% as the tungsten content increases toward equality with the molybdenum.

4. A cast molybdenum alloy capable of being worked at elevated temperatures and containing from .02% to 12% hafnium, not more than .75 carbon, less than .005 oxygen, not more than 5% titanium and not more than 1% zirconium, the balance consisting essentially of molybdenum.

5. A cast molybdenum alloy capable of being worked at elevated temperatures and containing from .02% to 12% hafnium, and .01% to .04% carbon, the balance consisting essentially of molybdenum.

References Cited by the Examiner Reinhold Publishing Corp., Chapman & Hall, Ltd., London, see especially Table 12.17 and Chemical Properties, pages 212-213.

DAVID L. RECK, Primary Examiner.

W. A. DOUGLAS, Examiner. 

1. A CAST ALLOY CONTAINING FROM .02% TO 12% HAFNIUM, .01% TO .75% CARBON, LESS THAN .005% OXYGEN, NOT MORE THAN 5% TITANIUM, NOT MORE THAN 1% ZIRCONIUM, AND THE BALANCE CONSISTING ESSENTIALLY OF A MEMBER FROM THE GROUP CONSISTING OF MOLYBDENUM AND MIXTURES OF MOLYBDENUM AND TUNGSTEN WHEREIN TH EMOLYBDENUM CONTENT IS AT LEAST EQUAL TO THE TUNGSTEN CONTENT. 